The present invention relates to an implantable intraluminal device. More specifically, the present invention relates to a radially self-expanding implantable intraluminal device which is particularly useful for repairing or serving as a conduit for blood vessels narrowed or occluded by disease or for use in other body passageways requiring reinforcement or the like.
Intraluminal devices or, more specifically, endovascular prosthesis, are known for treating stenosis, stricture, aneurysm conditions and the like. These devices, which include stents and grafts, are generally implanted by a mechanical transluminal procedure. Stents are devices designed to hold open a constricting vessel and generally are not designed as conduits or bypass devices. Intraluminal or endoprosthetic graphs, on the other hand, are designed as internal bypass devices which relieve stress from the surrounding vessel wall. Often, a device of this type is percutaneously implanted within the vascular system to reinforce collapsing, partially occluded, weakened or abnormally dilated localized sections of a blood vessel. Advantages of this method over conventional vascular surgery include obviating the need for surgically exposing, incising, removing, replacing, or bypassing the defective blood vessel. Stents are often used in combination with other endoprosthesis, such as intraluminal grafts. In some cases a stent is positioned at each end of the graft, thus allowing the graft to serve as a conduit or internal support to relieve stress from the vessel wall. The stents on each end serve to keep the lumen open and to anchor the graft in place. Attachment of the graft to the stent can be accomplished with hooks or sutures. In some instances, the stent is attached to only one end of the intraluminal graft. In this case the graft is allowed to xe2x80x9cfloatxe2x80x9d in the downstream direction of the vessel.
Structures which have previously been used as stents have included coiled stainless steel springs; helically-wound coiled springs manufactured from an expandable heat-sensitive material; expanding stainless steel stents formed of stainless steel wire in a zig-zag pattern; cage-like devices made from malleable metal; and flexible tubes having a plurality of separate expandable ring-like scaffold members which permit radial expansion of the tube. Each of these devices is designed to be radially compressible and expandable so that they will easily pass through a blood vessel in a collapsed state and can radially expand to an implanted size after the problem area has been reached. None of these devices is designed to retain fluid.
Each of the foregoing structures suffer from a number of disadvantages. To begin with, current stents are not designed to be contractible once deployed and therefore a great deal of care must be taken to properly position and expand the device to the appropriate size. Over expansion of a stent places unnecessary stress on an already damaged vessel. Under expansion of the stent may result in inadequate contact with the inner wall of the vessel and migration of the stent may occur.
Because the structures are designed to be delivered in a collapsed state within a blood vessel, it is difficult to ensure that the device, once deployed, will radially expand to the proper dimensions. For example, the expansion of a particular coiled spring-type stent is predetermined by the spring constant and modulus of elasticity of the particular material used to manufacture the coiled spring structure. These same factors predetermine the amount of expansion of collapsed stents formed of stainless steel wire in a zig-zag pattern. Likewise, prostheses formed from heat sensitive material which expands upon heating have a predetermined amount of expansion based upon the alloy utilized in their manufacture.
Another type of endovascular prosthesis consists of a thin wall textile radially fixed graft, which is folded up to fit inside an introducer sheath. The graft is manufactured to a predetermined diameter. If the graft is oversized, when displaced in the artery and subsequently expanded, the graft may not fully open leaving a fold or a crease in the graft which may further constrict an already narrowed or occluded blood vessel. On the other hands if the graft is too small in diameter, it will slide around in the vessel and disrupt blood flow.
As previously mentioned, intraluminal grafts are often used in combination with stents. Another disadvantage of the foregoing types of intraluminal devices is that once the device is deployed within the lumen, it is permanently and fully expanded and cannot be contracted for repositioning. It is advantageous to be able to realign an intraluminal graft which has been misdeployed through catheter malfunction or any other problem which may arise during the implantation procedure. Generally, the present intraluminal devices once fully expanded cannot be easily moved within the lumen without surgery.
When repairing blood vessels narrowed or occluded by disease, or repairing other body passageways, the device used in repairing or supporting the passageway must be flexible enough to negotiate the curves or bends of the body passageway. Most conventional endovascular prostheses do not have the requisite ability to bend so as to be advantageously placed within the vascular system.
Accordingly, it would be desirable to develop a new and improved intraluminal device and, in particular, an intraluminal vascular graft that can be expanded to a variable size to accommodate the size of the diseased portion of the vessel and prevent migration of the graft away from the desired location and provide support functions similar to conventional stents. The intraluminal grafts of the present invention are directed toward achieving this result as well as others including: preventing rupturing and/or erosion of the body passageway by the expanded graft; permitting tissue of an elongated section of a body passageway to be supported by an elongated graft; providing the necessary flexibility to negotiate the bends and curves of a vascular system; and being repositionable and adjustable even after being radially expanded within the lumen. Therefore, an intraluminal vascular graft which would overcome the foregoing difficulties and others while providing better and more advantageous overall results is highly desirable.
In accordance with the present invention, a new and improved radially self-expanding implantable intraluminal device is provided. More particularly, the present invention is formed from a hollow tubular braid which may be implanted intraluminally and thereafter radially self-expands to come in intimate contact with the inner surface of the lumen in which it is inserted.
The device is preferably used as an endovascular prosthesis in which the device relieves the stress of weakened blood vessel, although it may be used in a variety of body passageways to provide reinforcement of a supporting passageway or the like. The implantable intraluminal device is both radially and longitudinally flexible or bendable. When the tubular braid is elongated in the longitudinal direction, the diameter of the device is decreased so that it may be percutaneously implanted within a body passageway. Once the device has been properly positioned within the body passageway, it is permitted to radially self-expand or self-deploy to come in intimate contact with the interior surface of the body passageway.
The hollow tubular braid may be formed from a number of natural and synthetic materials, including collagen, thermoplastics and metals. More specifically, thermoplastics which are useful include polyesters, polypropylenes, polyethylenes, polyurethanes, or polytetrafluoroethylenes and combinations and mixtures thereof. Useful metallic substances include stainless steel, titanium and nichol-chromium alloys, among others. The hollow tubular braid is formed to be radially self-expanding by heat-conditioning the thermoplastic or metal fibers from which the device is made at a sufficient time and temperature to effectuate memory. The braid is heat-conditioned in a radially expanded or longitudinally compressed position to provide the radially self-expanding feature of the device. For example, if the thermoplastic chosen for making a tubular braid is polyester, the tubular braid is preferably heat conditioned at a temperature from about 200xc2x0 F. to about 700xc2x0 F. for approximately five to thirty minutes and subsequently cooled while being maintained in a radially expanded position, thereby effectuating memory within the braided device.
The type of braid used to form the tubular device may be varied. More specifically, the intraluminal device of the present invention may be formed from a simple three yarn tubular braid (two-dimensional braid) or may be formed from a three-dimensional braid. The braid may also include a yarn which is used to stiffen the tubular braided structure and provide a greater radially expanding force. The expanding radial force is preferably designed so that the intraluminal device will open up to be in intimate contact with the interior surface of the body passageway in which it is inserted and anchor itself thereto.
Generally, the fibers used to form the braid have a denier in the range of 20 to 500 denier, although deniers outside this range may have utility for specific applications. The force exerted by the device is non-rupturing, i.e., sufficient to open the device without causing damage to the vessel wall. The braid may be formed with a braid angle between 15xc2x0 and about 90xc2x0 and preferably about 54.50 to about 75xc2x0 with respect to the longitudinal axis of the braided structure. The braid angle is measured from the longitudinal axis of the braided device.
Once inserted into the body passageway, the intraluminal device will be permitted to radially self-expand and substantially conform to the shape and inner surface of the body passageway. The intraluminal device need not be perfectly sized to the vessel or passageway into which the device is inserted since the diameter of the device is infinitely variable in the ranges between its minimum diameter and its maximum diameter.
An advantage of the radially self-expanding implantable intraluminal device of the present invention is that once it is inserted and permitted to self-expand, the device may still be repositioned or realigned if not properly positioned within the lumen. A method of repositioning an implanted intraluminal device of the present invention includes introducing a guide wire having on its distal end a means or mechanism, such as a finger-like member, for grasping the braided device so that the device may be realigned to a proper position within the lumen. By pulling on one end of the intraluminal device of the present invention, the device will elongate in the longitudinal direction causing a decrease in diameter of the device such that it is free to move within the vessel, thereby permitting the device to be easily repositioned. Once in the repositioned location and no longer longitudinally elongated, the device of the present invention will once again radially self-expand to come into intimate contact with the inner surface of the lumen.
One method of producing a radially self-expanding implantable intraluminal device includes radially expanding a hollow tubular braid and subjecting the radially expanded braid to conditions of time and temperature sufficient to set the material in the radially expanded position. As a consequence of radial expansion, the device is shortened in length due to changes in the angle of the yarns with respect to the longitudinal axis. The braid is then permitted to cool while maintaining the braid in the radially expanded position. The heat source for heat conditioning the thermoplastic braid includes a convection oven, a heated mandrel, an infra-red light source or immersing the device in a hot liquid medium. The thermoplastic braid is preferably heated at a temperature of about 200xc2x0 F. to about 700xc2x0 F. for a time period of about five to thirty minutes. However, the heat parameters will vary depending upon the thermoplastic selected for forming the tubular braid. The heat conditioning of the thermoplastic yarns of the braid provides the intraluminal device of the present invention with memory to return the device to a radially expanded position following a reduction in diameter due to longitudinal expansion so that the device may be intraluminally inserted into a body passageway.
In an alternative embodiment of the present invention, the intraluminal device may also include a means for attaching the device to the inner surface of the lumen to provide additional anchoring of the device. Such attaching means may include small hooks which are integrally formed on the outside or extraluminal surface of the device during the braiding process. Preferably, the hooks are integrally formed in at least one end of the device, although, depending upon the procedure being performed, both ends may include hooks. Anchoring means may also be added as a separate component if desired.
A preferred form of the intraluminal device, as well as other embodiments, features and advantages of this. invention will be apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.